Phrags in H/ponics

[taipan]

I have 3 plants of Phrag.pearcei which are standing ( above the rim of the pot ) in water. They look ok & have since I got them about 3 years ago. If all goes well I will be adding some more "water loving " Phrags at the end of the year
I plan to move them to a full hydroponic set up & will most likely have water moving continually.Before people answer ( hopefullly someone will ) please take into consideration the following
In BKK the min.day temp would be mid to high 20's ( deg C ) Max.mid 30's deg C. The coldest it gets would be about 15 or 16 for a few hours before the sun rises - in December. Also the trough will be under shade cloth & open to the elements eg rain wind etc & in the coolest part that I can find
My questions are:-
1) Would there be a greater chance of evaporation taking place if the level of water in the trough was kept at half way up the pot.
2) Should I run the water to the level of the rim to stop the top portion of LECA from dying out too much
3) Should I run the water continually or have the pump set on a timer for running eg once every hour for say 10 to 15 minutes.
4)Would the placement of small pebbles on top of the Hydroton ( cant get Prime Agra in Thailand ) be of any help.
Any other info would be appreciated